This invention relates to a one-part structural adhesive composition which bonds metallic substrates at room temperature in a very short period of time and is also excellent in adhesive strength to plane surfaces and oily surface-adhesion properties. In other words, this invention provides a one-part adhesive composition which is quick curing and is capable of setting metal to metal and the like within a few minutes and reaching practical adhesive strength within a few hours. The adhesive composition has excellent adhesive strengths to plane surface as well as excellent oily surface-adhesion properties.
Epoxy resins have been generally used as non-solvent structural adhesive agents in a great quantity since they have excellent adhesive strength to plane surfaces. In the case of two-part type epoxy resins, there are problems in that it is necessary to weigh each component and mix them sufficiently immediately before use and to use all the mixed adhesive within a limited time, and the curing agents are harmful to human skin due to curing agents. In the case of one-part type epoxy resins, there are also problems in that they need a high curing temperature of 120.degree. C. or more and have a short shelf life, although they need no mixing operation and provide good workability.
On the other hand, acrylic structural adhesive agents have been recently used in some fields. These acrylic adhesives are a non-mixing two-part type comprising a primer and a main ingredient. The primer containing a curing accelerator is coated onto one adherent surface immediately before bonding, and then the main ingredient is coated onto the other adherent surface. These two surfaces are rubbed against each other to fit them. These adhesives are characterized by no need for mixing two components, good workability, bonding at room temperature in a short time and adhesive strengths comparable to epoxy resins. These adhesives have defects, however, in that two-step bonding operations are required, although they need no mixing, and also the primer containing a curing accelerator is very irritative.
The present invention provides an acrylic structural adhesive agent which is of the one-part type and which is less irritative and has excellent adhesive strengths to plane surfaces and excellent oily surface-adhesion properties.